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| 2. |
- Lunnan, Ragnhild, et al.
(författare)
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A UV resonance line echo from a shell around a hydrogen-poor superluminous supernova
- 2018
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 2:11, s. 887-895
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-poor superluminous supernovae (SLSN-I) are a class of rare and energetic explosions that have been discovered in untargeted transient surveys in the past decade(1,2). The progenitor stars and the physical mechanism behind their large radiated energies (about 1O(51) erg or 1O(44) J) are both debated, with one class of models primarily requiring a large rotational energy(3,4) and the other requiring very massive progenitors that either convert kinetic energy into radiation through interaction with circumstellar material (CSM)(5-8 )or engender an explosion caused by pair-instability (loss of photon pressure due to particle-antiparticle production)(9,10). Observing the structure of the CSM around SLSN-I offers a powerful test of some scenarios, although direct observations are scarce(11,)(12). Here, we present a series of spectroscopic observations of the SLSN-I iPTF16eh, which reveal both absorption and time- and frequency-variable emission in the Mg n resonance doublet. We show that these observations are naturally explained as a resonance scattering light echo from a circumstellar shell. Modelling the evolution of the emission, we infer a shell radius of 0.1 pc and velocity of 3,300 km s(-1), implying that the shell was ejected three decades before the supernova explosion. These properties match theoretical predictions of shell ejections occurring because of pulsational pair-instability and imply that the progenitor had a helium core mass of about 50-55 M-circle dot, corresponding to an initial mass of about 115 M-circle dot.
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| 3. |
- Blagorodnova, N., et al.
(författare)
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iPTF16fnl : A Faint and Fast Tidal Disruption Event in an E plus A Galaxy
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 844:1
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Tidskriftsartikel (refereegranskat)abstract
- We present ground-based and Swift observations of iPTF16fnl, a likely tidal disruption event (TDE) discovered by the intermediate Palomar Transient Factory (iPTF) survey at 66.6 Mpc. The light curve of the object peaked at an absolute mag M-g = -17.2. The maximum bolometric luminosity (from optical and UV) was L-p similar or equal to (1.0 +/- 0.15) x 10(43) erg s(-1), an order of magnitude fainter than any other optical TDE discovered so far. The luminosity in the first 60 days is consistent with an exponential decay, with L proportional to e(-(t-t0)/T), where t(0) = 57631.0 (MJD) and tau similar or equal to 15 days. The X-ray shows a marginal detection at L-X = 2.4(-1.1)(1.9) x 10(39) erg s(-1) (Swift X-ray Telescope). No radio counterpart was detected down to 3s, providing upper limits for monochromatic radio luminosities of nu L-nu < 2.3 x 10(36) erg s(-1) and nLn < 1.7 x 10(37) erg s(-1) (Very Large Array, 6.1 and 22 GHz). The blackbody temperature, obtained from combined Swift UV and optical photometry, shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He II and Ha emission lines, with FWHMs of about 14,000 km s(-1) and 10,000 km s(-1), respectively. He. I lines are also detected at lambda lambda 5875 and 6678. The spectrum of the host is dominated by strong Balmer absorption lines, which are consistent with a post-starburst (E+A) galaxy with an age of similar to 650 Myr and solar metallicity. The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales, as compared to other optically selected TDEs. The discovery of such a faint optical event suggests a higher rate of tidal disruptions, as low-luminosity events may have gone unnoticed in previous searches.
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| 4. |
- Singer, L. P., et al.
(författare)
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The Needle in the 100 deg2 Haystack : Uncovering Afterglows of Fermi GRBs with the Palomar Transient Factory
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 806:1
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Tidskriftsartikel (refereegranskat)abstract
- The Fermi Gamma-Ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi Gamma-ray Burst Monitor (GBM) instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target of opportunity mode for the intermediate Palomar Transient Factory (iPTF) in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: eight afterglow discoveries, two of which (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384 respectively) and had spectroscopically confirmed broad-line type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star, rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility (ZTF), we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.
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| 5. |
- Bellm, Eric C., et al.
(författare)
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The Zwicky Transient Facility : System Overview, Performance, and First Results
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
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Tidskriftsartikel (refereegranskat)abstract
- The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.
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| 7. |
- Taddia, Francesco, et al.
(författare)
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iPTF15dtg : a double-peaked Type Ic supernova from a massive progenitor
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Context. Type Ic supernovae (SNe Ic) arise from the core-collapse of H-(and He-) poor stars, which could either be single Wolf-Rayet (WR) stars or lower-mass stars stripped of their envelope by a companion. Their light curves are radioactively powered and usually show a fast rise to peak (similar to 10-15 d), without any early (in the first few days) emission bumps (with the exception of broad-lined SNe Ic) as sometimes seen for other types of stripped-envelope SNe (e.g., Type IIb SN 1993J and Type Ib SN 2008D). Aims. We have studied iPTF15dtg, a spectroscopically normal SN Ic with an early excess in the optical light curves followed by a long (similar to 30 d) rise to the main peak. It is the first spectroscopically-normal double-peaked SN Ic to be observed. Our aim is to determine the properties of this explosion and of its progenitor star. Methods. Optical photometry and spectroscopy of iPTF15dtg was obtained with multiple telescopes. The resulting light curves and spectral sequence are analyzed and modeled with hydrodynamical and analytical models, with particular focus on the early emission. Results. iPTF15dtg is a slow rising SN Ic, similar to SN 2011bm. Hydrodynamical modeling of the bolometric properties reveals a large ejecta mass (similar to 10 M-circle dot) and strong Ni-56 mixing. The luminous early emission can be reproduced if we account for the presence of an extended (greater than or similar to 500 R-circle dot), low-mass (greater than or similar to 0.045 M-circle dot) envelope around the progenitor star. Alternative scenarios for the early peak, such as the interaction with a companion, a shock-breakout (SBO) cooling tail from the progenitor surface, or a magnetar-driven SBO are not favored. Conclusions. The large ejecta mass and the presence of H-and He-free extended material around the star suggest that the progenitor of iPTF15dtg was a massive (greater than or similar to 35 M-circle dot) WR star that experienced strong mass loss.
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| 8. |
- Adams, S. M., et al.
(författare)
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iPTF Survey for Cool Transients
- 2018
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 130:985
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Tidskriftsartikel (refereegranskat)abstract
- We performed a wide-area (2000 deg2) g and I band experiment as part of a two month extension to the Intermediate Palomar Transient Factory. We discovered 36 extragalactic transients including iPTF17lf, a highly reddened local SN Ia, iPTF17bkj, a new member of the rare class of transitional Ibn/IIn supernovae, and iPTF17be, a candidate luminous blue variable outburst. We do not detect any luminous red novae and place an upper limit on their rate. We show that adding a slow-cadence I band component to upcoming surveys such as the Zwicky Transient Facility will improve the photometric selection of cool and dusty transients.
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